CSY’s energy specialist, Xin, looks back on a recent retrofit project and reveals what made our approach so successful.
“The Easthouses project is a whole-house, fabric-first retrofit of 26 BISF steel-framed council homes in Midlothian, aimed at improving energy efficiency, reducing heat loss and air leakage, and transitioning to low-carbon heating.
CSY’s role was initially to undertake the feasibility study and develop the preferred retrofit strategy, followed by acting as Retrofit Adviser during the construction phase to support the project’s quality assurance and delivery – applying PAS 2035 principles to an occupied, real-world site. This project highlighted the strengths of the PAS 2035 process and the challenges that arise when retrofit theory meets practice . In particular, these challenges include the unintended consequences that can arise, and the importance of effective collaboration between trades and stakeholders.
PAS 2035 Procedures
PAS 2035 is the British Standard for the retrofit of existing dwellings. It sets out a structured, risk-managed framework to ensure energy efficiency upgrades are properly assessed, designed, installed and monitored – minimising defects, unintended consequences (such as damp or overheating), and the performance gap.
It does not set energy targets; instead, it governs how retrofit projects should be delivered using a whole-house approach.
PAS 2035 ensures retrofit projects are delivered safely, systematically and to a consistent quality standard, prioritising building health, occupant wellbeing and long-term performance.
The PAS 2035 process provided us with a structured route from initial assessment through to design, installation and post completion review. The whole house approach helped to ensure that energy efficiency measures were considered in context, rather than in isolation. The roles of the Retrofit Assessor, Designer and Coordinator were fundamental in maintaining compliance and ensuring that risks were identified early.
However, the project also demonstrated that using PAS 2035 is not a static checklist exercise. As works progressed on site, we encountered conditions that could not be predicted at assessment stage, including existing fabric issues and variations between properties. This reinforced the importance of ongoing review, clear change control, and maintaining our involvement of the Retrofit Coordinator throughout the project.
Unintended Consequences
For our design team, a key learning outcome from the Easthouses project was the potential for unintended consequences when installing energy efficiency measures, particularly where existing buildings have historic defects or nonstandard construction. Interventions such as insulation upgrades and airtightness improvements altered the hygrothermal behaviour of the buildings, increasing the risk of moisture related issues if not carefully managed.
The project highlighted the importance of ventilation strategy, detailing, and sequencing of works. In several instances, minor changes in specification or workmanship had the potential to create disproportionate risks, underlining why PAS 2035 places such emphasis on risk pathways and whole dwelling performance. These experiences reinforced the need for regular site inspections, prompt reporting of emerging issues, and a willingness to pause and reassess rather than pushing works through to maintain programme.
Collaboration Between Trades
Effective collaboration between trades was critical to the success of the Easthouses project. The retrofit measures required close coordination between insulation installers, window and door contractors, ventilation specialists, and general building trades. Where communication was strong, interfaces were well managed and rework was minimised.
Conversely, the project demonstrated that a lack of shared understanding of PAS 2035 principles at trade level can lead to gaps in responsibility and quality risks. Trades often focus understandably on their individual scope, but retrofit delivery requires an appreciation of how each element interacts with others. Toolbox talks, joint inspections, and clear drawings and details proved essential in aligning expectations and improving outcomes.
Success in Retrofit
The Easthouses project reinforced that PAS 2035 adds real value when applied as an active management framework rather than a compliance exercise. Early and continuous engagement from all parties, particularly the Retrofit Coordinator, is essential. Unintended consequences cannot be entirely eliminated, but they can be significantly reduced through vigilance, collaboration, and a willingness to adapt.
Ultimately, this project demonstrated that successful retrofit delivery depends as much on people and communication as it does on technical design. Strengthening collaboration between trades and embedding PAS 2035 principles at site level will be critical to improving outcomes on future projects.”
– Xin Zhang (Architectural Designer)
